This invention relates generally to a connector for electronic equipment, and more particularly, to connectors and circuit boards for transmitting and receiving differential signal pairs.
Numerous types of connectors and circuit boards exist today for conveying differential signal pairs. Differential signal pairs include complementary signals such that if one signal in a differential pair switches from 0 V to 1 V, the other signal in the differential pair switches from 1 V to 0 V. By way of example, differential signals are used today in high speed serial data connectors (sometimes referred to as “HSSDC”). Certain conventional connector and circuit board arrangements utilize a contact or signal trace layout in which a first differential pair is defined as a “transmit differential pair” and a second differential pair is defined as a “receive differential pair”. The contacts for transmit and receive differential pairs are separated by a central ground contact. In the past, ground contacts were also positioned along outer sides of the contacts for transmit and receive differential pairs, thereby creating a balanced contact arrangement by locating ground contacts on both sides of the transmit differential pair contacts and on both sides of the receive differential pair contacts.
Recently, it has been proposed to modify the connectors and circuit boards to cease using the outer contacts as dedicated ground contacts. Instead, it has been proposed to use the outer contacts for other functions.
However, disconnecting the outer contacts from the ground plane has been found to create certain problems with signal transmission at high data rates, such as 1 Gbps and higher. In the above-described balanced conventional arrangement, positioning the transmit and receive differential pair contacts between corresponding ground contacts created a balanced or symmetric contact arrangement to afford a line of symmetry between the two contacts within the transmit differential pair and a line of symmetry between the two contacts within the receive differential pair. Thus, contacts of each differential pair were held in a balanced ground environment. Each signal contact creates an electromagnetic (EM) field as the signal is conveyed therethrough. In a balanced ground environment, the EM fields created by the contacts of a differential pair are equal and opposite. Thus the EM fields of the contacts of a differential pair are cancelled out in a balanced ground environment.
However, when the outer contacts are modified to no longer constitute dedicated ground contacts, the ground environment symmetry is eliminated. When the ground environment becomes asymmetric, the EM fields generated and experienced by each contact within a differential pair become asymmetric. As signals are conveyed through the contacts of a differential pair and are exposed to different EM fields, the signals become unbalanced. When transmitting at high speeds, the asymmetry negatively impacts various signal characteristics, such as increased EM interference, increased differential insertion loss, increased jitter, creating mismatch in the AC return path, introducing common mode energy, creating an unbalanced or common mode signal, and the like. The reduction in signal performance becomes quite noticeable at higher and higher data rates, such as over 4 Gbps.
Therefore, a need exists to provide symmetry for a connector assembly or circuit board that utilizes differential pairs, while still providing the ability to utilize non-signal contacts for functions other than being dedicated to ground. Certain embodiments of the present invention are intended to meet these needs and other objectives that will become apparent from the description and drawings set forth below.